NB 06 Radio Access Networks Cte en
NB 06 Radio Access Networks Cte en
NB 06 Radio Access Networks Cte en
Cisco public
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Enterprise RAN 9
Access to spectrum 9
Various enhancements supported by the standard make 5G perfectly suitable for emerging enterprise use cases
that demand better reliability, wider coverage, and low latency. Extended support in shared and unlicensed
spectrum makes 5G even more attractive for enterprises. In addition, 5G operates in new bands up to 60 GHz
as well as the legacy spectrum under 6 GHz.
This paper focuses primarily on how enterprises can use 5G-based radio access networks to enable new use
cases and also provides a high-level overview of the architectural options available for different types of
enterprise deployments.
Figure 1.
Use cases for the new Wi-Fi 6 and private 5G technologies
Wi-Fi 6 and soon Wi-Fi 6E, as well as private 5G, are various technologies that Enterprises can use to digitize
their businesses worldwide. These technologies are driven by the need for:
● Higher performance that will be necessary when students go to 4K and 8K video, as they will soon.
● Low latency, 15 milliseconds or less, required for immersive applications such as AR and VR.
● IoT scale that can help customers connect thousands of devices over both Wi-Fi 6 and private 5G.
When you have 100 devices in a 100-square-foot area, the interference level can be high. Private
cellular networks can help meet tighter Service-Level Agreement (SLA) requirements in addition to
higher throughput demands.
● Reliable mobility to enable better process automation. For instance, when to hand over and where to
hand over is up to the client. Sticky Wi-Fi client behavior can cause connection drops that lead to
Automated Guided Vehicles (AGVs) and robots freezing in the middle of their operation. Private 5G
networks can help address some of these limitations, enabling better reliability and augmenting of
existing Wi-Fi networks in the enterprise.
5G network architecture
A 5G network essentially consists of three elements: A packet core, a Radio Access Network (RAN), and User
Equipment (UE), as shown in the figure below.
Figure 2.
Elements of a 5G network
Packet core functions can be grouped into Control Plane Functions (CPF) and User Plane Functions (UPF).
● CPF implements user authentication, mobility management, subscriber management, access policy
management, etc.
● UPF is the gateway or entry point for the 5G data. UPF implements routing, classification, and traffic
policies for user traffic.
Individual functions of the packet core can be implemented as a single-box solution or as distributed physical
nodes. This logical decomposition depends on various factors such as the size of the deployment, scalability,
physical location, etc. In general, CPF and UPF can be deployed in different physical locations. CPF can be in a
centralized location such as a data center or Network Operations Center (NOC), while UPF can be onsite or in
an internet service provider’s point of presence.
Figure 3.
5G network architecture (Source: 3GPP)
RAN is the radio access layer. It implements all of the radio interfaces and call control functions.
UE denotes user equipment and consists of endpoints that connect to the cellular network.
● UE connection management: This includes initial radio access, synchronization between RAN and UE,
establishment of the radio connection, and connection maintenance. Once a radio connection is
established, the UE will exchange Non-Access Stratum (NAS) signaling with the packet core that may
include an authentication procedure, followed by establishment of an end-to-end PDU session
(user plane/data).
● Handling of user plane traffic: In 5G, data traffic from the network to UE and from UE to the network
enters or exits through the packet core. The packet core classifies the incoming packets and maps them
to the corresponding PDU session belonging to the UE. MAC headers are removed, and only the IP
datagrams are sent over the GTP-u tunnel established for the PDU session between the packet core and
the RAN system. The RAN system takes the IP datagrams and schedules over the radio interface to the
user. Unlike Wi-Fi, transmission in 5G RAN is based on fixed time slots (Frequency Division Duplex [FDD]
and Time Division Duplex [TDD] to be precise). Control information and user data together are packed in
each radio frame. More than one user can be scheduled at the same time in a radio frame, or slot. In
order to meet the SLA requirements of individual user sessions, the RAN scheduler implements Quality-
of-Service (QoS) scheduling policies. The goal of the scheduler algorithm is to maximize the spectral
efficiency of the system while maintaining the QoS requirements of individual sessions.
● Baseband processing: During downlink processing, information scheduled is modulated and mapped to
radio resource elements, and then the IQ symbols are generated for each antenna stream. During uplink
processing, received IQ symbols are demodulated, control information and the signaling is consumed by
the local stack components, and the data is tunneled toward the packet core.
● Radio interface: During the transmission interval, IQ symbols generated by the baseband are converted
to the RF signal that is then transmitted over the air. When it is time for reception, the RF signal received
from the UE is converted to IQ symbols for baseband processing.
5G RAN architecture
Essentially, 5G RAN consists of the following layers.
Layer 3 protocol stack includes Radio Resource Control (RRC), NG Application Protocol (NGAP), and Xn layers.
RRC is responsible for radio resource control, broadcast of system information, and the establishment,
maintenance, and release of the UE radio connection. NGAP enables NAS communication between UE and the
packet core. Xn enables peer-to-peer communication between two RANs for faster handovers.
Layer 2 protocol stack includes Packet Data Convergence Protocol (PDCP), Radio Link Control (RLC), and
MAC sublayers. PDCP is responsible for over-the-air data ciphering, anchoring data during handover, and
duplicating data packets over multiple redundant radio access paths for providing reliability. RLC handles over-
the-air segmentation/reassembly and retransmissions in case of loss of data over the air. MAC implements
scheduler, link adaptation, radio frame management, and Hybrid Automatic Repeat Request (HARQ) for block-
level retransmissions.
Physical layer implements the baseband processing functions such as modulation, waveform generation,
channel coding, etc. Generated digital samples are sent to the radio module to be transmitted over the air.
Earlier implementations of cellular systems integrated all these layers, including RF elements, into one device.
Later digital radio interfaces allowed the baseband to be separated from the RF unit. This allowed flexibility and
ease of installation in macro networks and large buildings. Pico and small cells continued to use the integrated
approach with external and internal antenna options.
If we carefully inspect the functionality of each layer of the stack, we can see that it is possible to centralize
parts of the functionality and distribute the rest. This approach allows you to manage the compute and
spectrum resources efficiently based on demand while minimizing interference, to improve per-user
throughputs and connection reliability, and to enable a better handoff experience for users.
Split RAN architectures
Several RAN system implementations use split RAN functionality based on 4G technologies but in a proprietary
manner. However, in the case of 5G, 3GPP, O-RAN, and other standardization bodies have come up with
various functional split options that allow functionality to be distributed between different elements, namely the
Central Unit (CU), Distributed Unit (DU), and Radio Unit (RU). As shown in Figure 5, several options are possible.
Split architecture also allows the use of generic compute platforms and off-the-shelf hardware to implement
the baseband functions, which helps drive down the cost of RAN solutions. Users can mix and match RAN
elements from various vendors based on quality and cost factors. Split architecture also allows future-ready
networks. A RAN can provide newer functionality with a software update on existing hardware. Deploying
different frequency bands would just be a matter of replacing radio units that are a fraction of the cost of a RAN
system without affecting other parts of the solution. This helps in reducing the CapEx and OpEx of the solution.
Split RAN is also often referred to as virtual RAN or vRAN, since the CU and DU elements are pure software
components that can be virtualized or containerized. However, the design complexity is a key trade-off
alongside cost and flexibility.
● Split option 2: Layer 3 functions are implemented in the CU. Layer 2 and Layer 1 are implemented in the
radio unit, also called the DRU. This enables the benefits of centralized Layer 3 and Self-Organizing
Networks (SON). This architecture is suitable for mmWave (FR2) implementations and for Non-
Standalone (NSA) deployments.
● Split option 7.2: This option can be seen as an extension to split option 2. In this option, Layer 3
functions are implemented in the CU. Layer 2 and upper Layer 1 functions are implemented in the DU.
Lower Layer 1 and radio functionality are implemented in the RU. This enables you to leverage the
benefits of centralized Layer 3 resource management and the benefits of centralized scheduling in Layer
2 and Layer 1 while distributing the radio-specific functionality into individual radio units.
Figure 6.
Split RAN (O-RAN/vRAN) architecture
Integrated cells would typically be used as a coverage extension to provide cellular coverage for small regions
where macro coverage is insufficient. In addition, dense small cell deployments can be used to address the
capacity needs of larger areas where the device population is concentrated. Integrated small cell architecture is
particularly suited for distributed branch connectivity and smart cities where the solution can be managed by a
service provider or the city.
Figure 7.
Integrated RAN architecture (small cells or pico cells)
Enterprise RAN
In the 5G specification, 3GPP has attempted to address the needs of enterprises along with traditional service
provider cellular use cases. Key use cases that are of interest to enterprises are:
Figure 9.
Manufacturing plant
● Efficient spectrum allocation: Centralized Layer 2 and Layer 3 allows the spectrum to be allocated
among RUs based on channel conditions and load conditions at each RU.
● Better interference management: Centralized Layer 2 scheduling allows co-channel interference to be
managed efficiently by distributing resource blocks among users on individual RUs where the
interference could be high.
● Improved signal strength: Centralized Layer 2 scheduling allows joint transmission of the same data
stream from multiple RUs to the same user if the user has overlapped coverage from multiple RUs. With
this technique the user would experience significant channel gains, resulting in improved signal strength
and the ability to operate at higher modulation and code rates than were possible previously.
● Uniform coverage: Due to overlapping coverage and centralized Layer 2 scheduling, users would
experience uniform coverage, whether at the cell center or cell edge. Regardless of user location,
throughput would remain uniform.
● Elimination of handovers: The probability of connection loss during handovers is higher due to changing
channel conditions. The handover process involves off-channel neighbor cell measurements and
interactions between the serving cell and the target cell. These add to the latency and handover time. By
employing an architecture that configures a group of radios to act as single cells, wherever the UE may
be, it will be served by the same cell. It appears as if the network is following the user. Because of this,
when UE moves from the coverage area of one RU to the coverage area of another, it will not experience
any handovers. Configuring a group of radios to act as a single cell is just one of the many options for
how the RAN architecture. This configuration options should only be employed for coverage area(s) of
the network serving mission-critical applications
● Greater connection reliability: Uniform coverage and applying a configuration to a group of radios to act
as a single cell to achieve zero handovers can minimize the block error rate, which helps improve the
reliability of the connection and provides low user plane latency.
● Increased system capacity: Due to increased spectral efficiency of 4G and 5G technology. By applying
smart RF design to and reduce interference and utilizing advanced RF performance features of 4G and
5G, more users can be handled and per-user throughput can be increased significantly at the system
level.
● Centralized resource management allows better slice management, admission control, and SON
capabilities.
● Upgradability: Support for newer RF bands, additional features, and 3GPP release upgrades can be
easily supported with a software update on the DU. In the worst case only the RU hardware needs to be
replaced, which is much cheaper than a complete replacement of the RAN system.
● Cost of solution: Typical coverage needs are much smaller compared to industrial/manufacturing
deployments. Fewer small cells are sufficient to address the coverage needs, helping reduce the costs.
● Deployment simplicity: Reduction in the number of boxes simplifies deployment and reduces
management complexity. Zero-touch deployment can be easily achieved.
● Ease of integration with existing network: Since integrated small cell architecture doesn’t involve
fronthaul, the LAN is relieved from stringent network latency and jitter requirements. This means that
expensive network replanning and upgrades are not absolutely needed. Small cells can be deployed on
the enterprise’s existing network infrastructure.
Figure 10.
Distributed enterprise
● The typical coverage area of a small cell operating on 3.5 to 3.8 GHz would be around 15,000 square
feet with decent cell edge performance. Thus, many cells are required to cover a typical factory floor of
1 or 2 million square feet. This means robots and AGVs experience lots of handovers in their journey
from one end of the building to the other. Handovers affect reliability and also increase user plane
latency at the time of handover.
● The RF design, spectrum management and coordination of a large number of small cells is often a
challenge, typically leading to more interference and lower efficiency in terms of bits/Hz.
Together, Wi-Fi 6 and 5G can enable businesses to drive digital transformation. In general, Wi-Fi is easier to
deploy and can be deployed as a standalone system. Wi-Fi is enabled in a vast number of client devices that
are readily available at optimal cost. On the other hand, 5G is complicated and involves multiple elements to
deploy. This may require reskilling of enterprise IT managers. In addition, global availability of spectrum for
private 5G enterprise deployments is also limited. Initially, the cost of network equipment and client devices is
also comparatively much higher. However, both 5G and Wi-Fi are needed to provide ubiquitous coverage as
well as better mobility and have distinct application areas across various verticals including manufacturing,
retail, hospitality, healthcare and industrial IOT. 5G and Wi-Fi can coexist in a single deployment and
complement each other. For example, in a manufacturing facility, 5G can be used for mission-critical
applications and Wi-Fi can be used for employee and guest internet access. In a healthcare facility, 5G can be
used for the nurse call system and for transferring data from health monitoring systems, and Wi-Fi can be used
for regular internet and office communications.
Figure 11.
5G and Wi-Fi coexistence
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